The present invention relates generally to a radio antenna and, more specifically, to an internal multi-band antenna for use in a hand-held telecommunication device, such as a mobile phone.
The development of small antennas for mobile phones has recently received much attention due to size reduction of the handsets, requirements to keep the amount of radio-frequency (RF) power absorbed by a user below a certain level regardless of the handset size, and introduction of multi-mode phones. It would be advantageous, desirable and even necessary to provide internal multi-band antennas to be disposed inside a handset body, and these antennas should be capable of operating in multiple system such as E-GMS900 (880 MHz-960 MHz), GSM1800 (1710 MHz-1880 MHz), and PCS1900 (1859 MHz-1990 MHz). Shorted patch antennas, or planar inverted-F antennas (PIFAs), have been used to provide two or more resonance frequencies. For example, Liu et al. (Dual-frequency planar inverted-F antenna, IEEE Transaction on Antennas and Propagation, Vol.45, No.10, October 1997, pp. 1451-1458) discloses a dual-band PIFA; Pankinaho (U.S. Pat. No. 6,140,966) discloses a double-resonance antenna structure for several frequency ranges, which can be used as an internal antenna for a mobile phone; Isohatala et al. (EP 0997 974 A1)discloses a planar antenna having a relatively low specific absorption rate (SAR) value; and Song et al. (Triple-band planar inverted-F antenna, IEEE Antennas and Propagation International Symposium Digest, Vol.2, Orlando, Fla., Jul. 11-16, 1999, pp.908-911) discloses a triple-band PIFA.
Currently, the antenna is one of the largest parts in a mobile phone. In order to fit more antenna elements with acceptable performance in the available space, there is an ongoing effort to reduce their physical size. As the size of the mobile phone decreases, the radiation efficiency of traditional small internal handset antennas also decreases, particularly in an antenna system that has wavelengths corresponding to a resonance frequency below 1 GHz. The reduction in radiation efficiency is due to the fact that the radiation resistance of the antenna is very small compared with the radiation resistance of the chassis. This means that a substantial part of the radiation is caused by the chassis currents and a relatively small part of radiation is attributable to the antenna. Furthermore, when the ground plane of a planar antenna in the handset is sufficiently small, the reactive near fields of the antenna surround the ground plane. Consequently, the currents on the ground plane are substantially uniform on both sides of the ground plane. This phenomenon becomes noticeable when the size of the ground plane in the handset is smaller than one-third the resonance wavelength. Locating the internal antenna on the back of the handset does not sufficiently improve the specific absorption rate (SAR) characteristics caused by the ground-plane currents of the antenna. With internal antennas, the currents on the antenna element yield only moderate SAR values to the user""s head. The relationship between the resonance wavelength and the size of the ground plane renders it difficult to design an internal antenna with high efficiency, especially for a GSM900 system. However, with a GSM1800 system, the resonance wavelength is usually smaller than the size of the ground plane.
It is advantageous and desirable to provide a three-band internal radio antenna for use in a mobile phone capable of operating in multiple systems such as E-GSM900, GSM1800 and PCS1900. The antenna is simple to produce and, at the same time, the SAR characteristics of the antenna are also improved.
According to first aspect of the present invention, a multi-band radio antenna structure for use in a hand-held telecommunication device comprises:
a ground plane;
a first planar radiating element formed of a first electrically conducting area having a first resonance frequency, wherein the first planar radiating element has a grounding point and a feed point for feeding adjacent to the ground point;
a second planar radiating element formed of a second electrically conducting area having a second resonance frequency substantially lower than the first resonance frequency, wherein the second electrically conducting area has a grounding end connected to the first electrically conducting area adjacent to the grounding point of the first planar radiating element, and an open end surrounding at least two sides of the first electrically conducting area, leaving a gap between the second electrically conducting area and the surrounded sides of the first electrically conducting area; and
a third radiating element formed of a third electrically conducting area adjacent to the second planar radiating element having a third resonance frequency generally higher than the first resonance frequency, wherein the third electrically conducting area has a further grounding point.
Preferably, the first, second and third electrically conductive areas are co-located on a common plane.
Preferably, one section of the open end of the second electrically conducting area is extended beyond an edge of the ground plane.
According to the present invention, the first resonance frequency is substantially in a frequency range of 1710 MHz to 1880 MHz, the second resonance frequency is substantially in a frequency range of 880 MHz to 960 MHz, and the third resonance frequency is substantially in a frequency range of 1850 MHz to 1990 MHz. The third resonance frequency, in general, is higher than the first frequency, but their frequency ranges have an overlapping section.
According to the second aspect of the present invention, a hand-held telecommunication device capable of operating at multi-band frequencies, said hand-held telecommunication device comprises:
a housing including a front portion and a back cover;
a chassis disposed in the housing between the front portion and the back cover, wherein the chassis has a back side facing the back cover and an opposing back side having a ground plane, and wherein the ground plane has a top edge located adjacent to a top end of the housing; and
an antenna structure comprising:
a first planar radiating element formed of a first electrically conducting area having a first resonance frequency, wherein the first planar radiating element has a grounding point connected to the ground plane and a feed point for feeding adjacent to the ground point;
a second planar radiating element formed of a second electrically conducting area having a second resonance frequency substantially lower than the first resonance frequency, wherein the second electrically conducting area has a grounding end connected to the first electrically conducting area adjacent to the grounding point of the first planar radiating element and an open end surrounding at least two sides of the first electrically conducting area, leaving a gap between the second electrically conducting area and the surrounded sides of the first electrically conducting area, and wherein the open end has an extended portion adjacent to the top end of the housing and extended beyond the top edge of the ground plane.
Preferably, the antenna structure further includes a third radiating element formed of a third electrically conducting area adjacent to the second planar radiating element having a third resonance frequency generally higher than the first resonance frequency, wherein the third electrically conducting area has a further grounding point.
Preferably, the first, second and third electrically conductive areas are co-located on a common plane.
According to the third aspect of the present invention, a method of improving radiating efficiency and characteristics of a multi-band antenna structure in a hand-held telecommunication device, wherein the hand-held telecommunication device has
a housing including a front portion and a back cover;
a chassis disposed in the housing between the front portion and the back cover,
wherein the chassis has a back side facing the back cover and an opposing front side having a ground plane, and wherein the ground plane has a top edge located adjacent to a top section of the housing; and
an antenna structure comprising:
at least two planar radiating elements, wherein
the first planar radiating element is formed of a first electrically conducting area having a first resonance frequency, and wherein the first planar radiating element has a grounding point connected to the ground plane and a feed point for feeding adjacent to the ground point; and
the second planar radiating element is formed of a second electrically conducting area having a second resonance frequency substantially lower than the first resonance frequency, wherein the second electrically conducting area has a grounding end connected to the first electrically conducting area adjacent to the grounding point of the first planar radiating element and an open end surrounding at least two sides of the first electrically conducting area, leaving a gap between the second electrically conducting area and the surrounded sides of the first electrically conducting area, and the open end has an extended portion adjacent to the top end of the housing. The method comprises the steps of:
disposing the ground plane away from the top end of the housing for providing a further gap between the top edge of the ground plane and the top end of the housing; and
disposing the antenna on the chassis such that the extended portion of the open end of the second electrically conducting area is extended beyond the top edge of the ground plane over the further gap between the top edge of the ground plane and the top end of the housing.
Preferably, the antenna structure further includes a third radiating element formed of a third electrically conducting area adjacent to the second planar radiating element having a third resonance frequency generally higher than the first resonance frequency, wherein the third electrically conducting area has a further grounding point.
The present invention will become apparent upon reading the description taking in conjunction with FIGS. 1 and 3.